a. Field of the Invention
This invention relates generally to the paving of roads, airport runways, parking lots, and the like, and more particularly to new and improved apparatus and methods which can be employed on conventional paver finisher apparatus for making long life, fully compacted, high density longitudinal joints between first and second adjacent mat sections of paving material, such as asphalt paving material.
b. Background of the Invention
One of the major problems in asphalt paving, either overlay or for a new roadway, is obtaining sufficient density and a good seal at the joint between the adjacent passes of paving material in order to provide a long life longitudinal joint. A generally satisfactory, long life longitudinal joint can be produced by operating two pavers working simultaneously. When doing this the lead paver usually runs 50 to 100 feet ahead of the other. The following paver matches the joint of the lead paver before the roller compacts the joint. A good quality joint results because both mat sections are fused together while both mat sections are still hot when rolled.
There has been a serious and continuing problem in obtaining a long life, longitudinal joint between a first mat section of previously laid, rolled and compacted paving material (a cold mat section), and a second mat section of newly laid, fresh and hot paving material (a hot mat section). Since the edge of the first, earlier laid mat section is not restrained during rolling of the first mat section, paving material falls from the side and forms an edge region which angles downwards, generally at an angle of about 45 degrees, and is of lower density than the balance of the rolled and compacted material of such first mat section. Prior attempts to form a long life longitudinal joint between the previously laid cold mat section and the newly laid hot mat section of fresh paving material have heretofore not been entirely successful.
The most commonly used method of paving adjacent lanes, is to use a single paver finisher machine. When a single paver lays both mats sections, the first mat section is laid and then rolled to compact the paving material. When the second mat section is laid adjacent the first mat section, there has usually been sufficient passage of time that the material of the first mat section is cold and there is no longer the desirable fusing together of hot paving materials to form the joint such as when two paver finisher machines are operating simultaneously.
In accordance with this commonly used method, a first pass is made with the paver finisher machine to lay the first lane. This first lane is then rolled to compact the paving material thereof. The second lane, or mat section, is then laid with the paver finisher machine being accurately steered to match the second pass to the first rolled and compacted lane sometimes with an desired overlap. When the second mat section is laid adjacent a first mat section which has been rolled and compacted and which has cooled (cold mat section), this overlap must be removed prior to the rolling to compact the paving material of the second mat section. The depth of the new mat section must be such that subsequent compaction with the roller will bring the new mat section down to the level of the existing first rolled mat section. Even when very carefully laid, the longitudinal joint so produced between the two adjacent lanes is not entirely satisfactory. Inadequate compaction of the joint is a common cause of joint failure. Often, handwork is required to complete the joint, which is costly, time consuming, and dangerous to the workers, and still fails to produce an entirely satisfactory high density joint.
Examples of some other prior methods, none of which have produced an entirely satisfactory longitudinal joint with a previously laid and rolled cold mat section, are: (1)pre-heating the low density edge region of the cold mat section just prior to the laying of the new mat section of fresh hot paving material, and (2) cutting away the sloping, low density edge region of the cold mat section to form a vertical or undercut edge surface prior to laying the new mat of fresh paving material adjacent the cold mat section. Another prior art method which also fails to produce an entirely satisfactory long life, high density joint, is shown in U.S. Pat. No. 4,181,449. The apparatus and method of U.S. Pat. No. 4,181,449 involves forming a tapered joint between the two adjacent asphalt mat sections formed by two wedge shaped, compacted overlying layers. Such tapered joints are prone to separation and raveling and consequent shorter than desired life.